Have you thought about Near-Space Tourism? Basically, instead of building the DSS first, you build a dedicated hotel. That would bring in plenty of revenue for you to build the DSS. Also, commercial flights on the Atmospheric Ascender.

The altitude requirements for a near space hotel are a lot lower than that of a launch facility for the Orbital Airship. 20km should be high enough to offer a Dark Sky view. The air hotel can then be a lot smaller.